This invention relates to a sealing device of a fuel injection unit which provides improved sealing between component parts of the unit.
A conventional fuel injection unit for internal combustion engines is provided with a delivery valve as shown in FIG. 1, which comprises a valve body A, a delivery valve holder B in which the delivery valve A is accommodated, and a valve seat C fitted into an open end of the valve holder B in an airtight manner, as is known e.g. from Japanese Provisional Patent Publication (Kokai) No. 57-183561. A coiled spring E is provided within a valve-receiving bore D formed in the valve holder B and urges the valve body A so that the valve body A is axially moved by pressurized fuel from a pump section, not shown, against the force of the spring E.
According to the known fuel injection unit, as shown in FIG. 2, an open end face of an end portion Ba of the valve holder B opposed to a flanged portion Ca of the valve seat C has a radially outer slant face Ba1 moderately outwardly Slanting at an angle of approximately 15 degrees with respect to a plane F defined by the open end face of the valve holder B, in order to improve the sealability between the valve holder B and the valve seat C.
However, during operation of the fuel injection unit, when air bubbles are developed due to a certain factor in fuel oil within a fuel chamber, not shown, of the pump section, and carried by fuel oil into the interior of the valve holder B, they are moved to the end portion Ba of the valve holder B which is in contact with the valve seat C.
However, a radially inner slant face Ba2 is formed on the open end face of the end portion Ba of the valve holder B and moderately inwardly slanting at an angle of approximately 15 degrees with respect to the open end plane F of the valve holder B. Since the angle of the radially inner slant face Ba2 relative to the open end plane F is small, the air bubbles moved to the open end portion Ba are apt to be caught and collect in a gap between the radially inner slant face Ba2 and the opposed face of the flanged portion Ca of the valve seat C. As a result, when the collected air bubbles break, there takes place so-called cavitation erosion in the radially inner slant face Ba2 and the opposed face of the flanged portion Ca of the valve seat C, which causes degraded sealing between the valve holder B and the valve seat C.